Process for the production of naphthalene



Dec. 3, 1963 A. SCHMALENBACH 3,113,161

PROCESS FOR THE PRODUCTION OF NAPHTHALENE Filed April 16, 1958 'l. 'IIIIIIIQ ADOLF SCHMALENBACH w walwuw ATTORNEYS United States Patent 3,113,161 PROCESS FOR THE PRODUCTION OF NAPHTHALENE Adolf Schmalenbach, 22 Bosselberg, Essen, Germany Filed Apr. 16, 1958, Ser. No. 728,877 Claims priority, application Germany July 11, 1953 3 Claims. (Cl. 260-674) This invention relates to the art of producing naphthalene. More particularly, this invention relates to a process in which a naphthalene hot-pressing material is produced from a starting product containing crystallized naphthalene by using a continuously operating worm press or the like.

It has recently been proposed to use a continuouslyoperating worm press for the separation of naphthalene from naphthalene oil. This process made possible the production of a naphthalene of at least the quality of hotpressing material, i.e., having a soldification point higher than 79 C. without the necessity of using, apart from actual compression, the means previously employed. For example, it was. previously thought necessary to employ an intermediate crystallization, in, for instance, ladles, followed by reheating, chemical washings, redistillation and final communition in order to accomplish the purpose of the process.

These disadvantages of such techniqus have been overcome by the use of a continuously-operating worm press. The improvement depends on the fact that during the pressing operation a constant kneading of the crystallized mass takes place with displacement of the crystals relative to one another. There is thereby obtained a greater degree of separation of the oily tactions than was forrnerly the case. In place of a Worm press, it is of course possible to use other pressing means, such as extrusion presses, thrust centrifuges, worm centrifuges or the like, the essential requirement being that the material is moved during the pressing operation and is subjected to high pressures in comparatively thin layers.

In such processes, oil is expressed through apertures in the housing wall of the worm press (such as slots, holes, or the like) and is thereby removed from the crystalline naphthalene which is produced. I have now discovered that the expressed oil is not completely unitorm over the length of axis of expression. The properties of the expressed oil, for example, its solidification point are in certain circumstances essentially dependent upon the place at which the expressed oil flows out of the press housing. I have established that the expressed oil discharging at the commencement of the pressing operation, i.e., in the vicinity of the supply device for the crude product, has in certain circumstances a solidification point of only 2045 C. This is considerably lower than the solidification point of the expressed oil which is discharged at later stages in the pressing operation, i.e. in the vicinity of the discharge end of the press. While I do not wish to be bound by the theory, I believe that this phenomenon is at least partially due to the tact that as the naphthalene progresses through the press, the material is gradually heated due to the pressing energy being converted into heat and apparently also heat developed by frictional torces, so that the oil discharged at a later stage in the pressing has a greater proportion of naphthalene than at the beginning.

I have further found that the expressed oil discharging at the end of the pressing operation has a lower content of thionaphthe-ne than the expressed oil obtained at the start of the pressing operation.

Accordingly, it is an object of this invention to utilize the above discovery and to provide a process therefor.

More particularly, it is an object of this invention to reduce to an extent greater than formerly possible the 3 1 13,161 Patented Dec. 3, 1963 content of oily constituents and thionaphthene in the naphthalene final product and thereby raising the solidification point of the naphthalene obtained in greater overall yield.

A further object of this invention is to provide a process for the production of naphthalene from naphthalene oil by cooling and passing such oil through a continuous pressing zone and recovering from said zone an expressed oil, and wherein said expressed oil is recovered in at least two portions, the first of said portions being an oil fraction low in naphthalene content and rich in thionaphtheme and the second of said portions being an oil fraction rich in naphthalene, and thereafter admixing said second portion rich in naphthalene with untreated naphthalene oil for subsequent pressing operations.

It will therefore be seen that an object of this invention also includes a process which provides for a recovery of the naphthalene content from naphthalene oil while maintaining the desired high solidification point of the crystalline naphthalene products, to a greater extent than has hitherto been possible.

Still another object of this invention is to provide an apparatus suitable for carrying out the above process.

Additional objects of this invention Will be apparent from the following specific description thereof:

Broadly speaking, this invention comprises cooling a naphthalene oil to a temperature lower than 60 C., preferably to room temperature, and thereby forming crystals. These crystals are then supplied in the :form of solid lumps or as a comparatively stiff paste to the press. During the operation of the press, the oil is expressed from the crystalline material and discharged through the openings in the cylindrical external wall of the press. The crystalline material is then discharged at the outlet end of the press.

The press is so designed and constructed that over the length of the pressing operation there will be a variation in the pressures applied to the material therein. This can be achieved by suitable design of, for instance, a Worm press. Thus, as one skilled in the art will appreciate, the pitch of the worm in the press may be varied over the length thereof to accomplish this variation in pressing pressures. It is also possible and is contemplated tor the practice of this invention, to provide a worm press having two separate worm screws therein which are functionally connected in series but structurally separate (from one another and operated so as to provide the pressing pressure variations. It is advantageous to use a lower pressing pressure in the first press than in the second press. Where a single WOHH screw is employed, the pitch of the worm is greater in the vicinity of the supply of the comparatively cold crude products than at the middle of the Worm. It is advantageous to again increase the pitch of the worm towards the discharge end of the press. The result of such variations in pitch is that higher pressures are set up at the beginning of the worm, i.e., in the zone wherein the crude product is introduced and is still comparatively cold, and also at the discharge end of the press so that the remaining naphthalene oil in the comparatively dry crystals will be expressed as completely as possible. There will also be obtained substantially equal linear quantitative discharge of the oil over the length of the press.

In the above operations, the temperature of the crystallized material when introduced will preferably be no lower than 15 20 C. and a temperature of about 40 C. is still preferred. In the case of the application of temperatures lower than 40 C. e.g., 25 C., there will be a decrease in the quantity processed by the press, with a given motor output, per unit of time. This results from the fact that the solid material is more difiicult to press due to its greater hardness. However, the solid product thereby obtained has a solidification point which rises to 799 C., corresponding to a naphthalene content of 99.1%. On the other hand, if the temperature of about 55 C. is chosen for the raw material on introduction to the press, then greater quantities of the raw naphthalene can be processed per unit of time because of the softer and more pliable material.

The quality of the naphthalene produced in this latter embodiment is not quite as high, however, and will have a solidification point of about 79 C. The yield will also decrease somewhat to about 52% since a rela tively large amount of naphthalene will be dissolved in the expressed oil due to the higher temperatures. The substantial improvement and purification of the product will be appreciated when it is recognized that the solidification point of the raw naphthalene will be between about 60-75 C. Naphthalene having a solidification point of 79 C. has a purity of about 97.1%. Generally, I prefer not to employ a raw naphthalene starting material having a solidification point less than 65 C.

During the pressing operation, the expressed oil discharged from the press is collected in two portions. I have found that the portion discharged in the first zone of the worm press will have a lower solidification point and lower naphthalene content than portions obtained at a later zone in the press. Accordingly, I provide in this invention a method of separating the two separate portions of oil so that the expressed oil having the higher naphthalene content is obtained separately from the less valuable oil. This second portion of oil is then recycled to the original crude naphthalene oil starting material prior to its introduction into the worm press.

This technique enables a far greater yield recovery of purified naphthalene crystals from a given naphthalene crude oil starting material. Not only is the feed to the worm press thereby enriched in naphthalene content, but the concentration of thionaphthalene is at the same time reduced since I have found that this material will be largely removed from the crude material in the initial phase of the pressing operation.

Operating according to the present invention will in many circumstances provide yields and purity of the naphthalene crystal products greater than those which can be achieved by the conventional separation of naphthalene from naphthalene oil by distillation.

Referring now to the drawings, there is there'illustrated an apparatus which may be employed for the practice of this invention. It will be appreciated of course that the process is not limited to specific apparatus shown, but may be carried out in other equivalent means so long as substantially the same functional arrangement is present. That is, as noted above, extrusion presses, thrust centrifuges, worm centrifuges, and

the like may be employed. Such alternative apparatus can be readily adapted to achieve the desired pressing pressure variation which is described with reference to the worm press, as one skilled in the art will appreciate. The apparatus illustrated consists of a screw press'l, fitted with a conical housing, formed of pipes 3 held together by bands 3a, the taper diminishing in the direction of the discharge mouth 2. The screw 4 is mounted on a hollow shaft 5, passing through the housing 3 of the press at its wider end and rotatably mounted in a stufiing box 6. On the shaft 5 there is fixed a toothed wheel or similar device (not shown) which is driven by a prime mover (not shown) for the screw press. Two pipes, 8 and 9 are connected from the outside to the hollow shaft 5 of the press and serve for the admission or discharge of a liquid or gaseous cooling or heating medium. By suitably adapting the temperature of the medium fed by pipe 8 and drawn ofi by pipe 9, it is possible to regulate the temperature of the raw material to be pressed inside the press-housing according to the most favorable degree for pressing.

The aperture of the mouth 2 of the press can be calibrated by a mouth-piece 13. This mouth-piece 13 is adjusted by means of a spindle 14 in such a Way that in the press such pressures are established as required for reaching the desired solidification point of the naphthalene. During the operation of the press, the solid naphthalene is conveyed to the mouth 2 to a chute 15 from which it falls onto a conveyor belt 16 transporting the naphthalene to the point for further handling.

The raw material to be pressed is fed through a feeding hopper 17. To this the raw naphthalene is fed over a chute 18. A cooling drum 19 feeds the raw material to the aforesaid chute 18. The cooling drum 19 consists of a cylindrically shaped metallic drum maintained by inner cooling with water at a temperature below the solidification point of the naphthalene, preferably below 60 C. This cooling drum turns at a relatively low speed, e.g., a few revolutions per minute, and is partially emersed in a trough 20 filled to a certain level with the liquid naphthalene oil 21, which is the crude starting material.

Owing to the low temperature of the surface of drum 19 solid naphthalene is separated thereon in crystallized form and forms a more or less thick coherent layer on the outside of the cooling drum. This layer is removed from the cooling drum 19 by a scraper 22 in such a way that a comparatively course material is obtained which is fed by way of the chute 18 to the feeding hopper 17 and from there to the screw press, as indicated by the path arrows.

Mounted underneath the press 3 is a trough generally indicated as 31 having a bottom wall 23 and separated into two sections by partition wall 25 so that the expressed oil is collected in two portions 30 and 29. The portion 30 which is the first expressed oil is removed through pipe 12. The second portion 29 passes through pipe 10 to mixer 24 where it is admixed with fresh naphthalene oil introduced through pipe 11. If desired, cooling means (not shown) can be provided at line 10 intermediate the trough and the mixer 24. The mixture is then passed through pump 27 and line 28 to trough 20. Thus, expressed oil in portion 29 is recycled through the system to permit full recovery of the desired naphthalene product.

The following example will illustrate one method of practicing my invention, but it will be understood that the invention is not limited to the specific amount of materials or conditions set forth therein.

Example As starting material, there was used a naphthalene oil obtained from fractional distillation of coal tar. The fraction had a solidification point of 701 C. and a naphthalene content of 78.2%.

Seventeen tons of this oil was transmitted through pipe 11 to the mixer 24, which was kept at a temperature between 71 and 75 C. This naphthalene oil contained 13.29 tons of naphthalene. Simultaneously, 7.2 tons of pressed oil was collected at 29 transmitted through pipe 10 into the mixer 24. Partition wall 25, dividing the trough 31 into two sections was so aligned, that the pressed oil accumulating at 29 manifested a mean solidification point of about 70 C. In the case under consideration, partition wall 25 was positioned at a point somewhat more than -73 the length of the press housing from mouth 2. The mixture of initial naphthalene oil and reconducted pressed oil was transmitted via pump 27 through pipe 28 to trough 20, in which it was cooled to a temperature of about 40 C. Hereby the entire material solidified on cooling drum 19, forming a crystal mass which after being stripped off cooling cylinder 19 by scraper 22, manifested a grain size of between 0.4 and 2 cm.

The crystal mass was poured through filling funnel 17 into horizontally-aligned screw press 1. The screw press had a length of about cm. and an inner diameter of about 25 cm. within the range of filling funnel 17, and about 20 cm. in the proximity of mouth 2. The outer jacket of the screw press consisted by and large of horizontally-arranged metal rods 3, which were fastened by means of the corresponding fastening rings 3a into a bundle which tapered conically toward the end of the press. The width of the slots between each two adjacent metal rods was an average of 0.2 mm.

As soon as the pressing process was completely in action, pure, solid naphthalene was discharged at mouth 2 of the press. Inside the press, in the proximity of filling funnel 17, the temperature was about 40 C., corresponding to the temperature of the filled material. Then the temperature rises rather uniformly to 74 to 75 C. up to mouth 2 of the press 1. This rise in temperature is due to the heat produced by pressure and frictional forces.

The 24.2 tons of initial material, consisting of 17 tons of naphthalene oil and 7.2 tons of reconducted pressed oil, yield the following products after completion of pressing:

(solidification point: 70.1 C.) 72 (3) Part of pressed oil 30 that is removed in the process (solidification point: 60 C.) 8.8

Thus 8 tons of pure naphthalene with a solidification point of 792 is produced from the 13.29 tons of naphthalene (=17 tons raw naphthalene oil) introduced in the process. This corresponds to a yield of 60.2%.

By way of contrast, I have also operated the press according to the above conditions but without separation and recycling of the expressed oil. Starting here with 24 tons of raw naphthalene oil, at a temperature of 40 C., instead of 17 tons as described above, the oil can be processed in approximately the same time. From this starting material which contains about 78.2% of naphthalene or 18.77 tons, there is obtained, however, only about 42.6% recovery. Thus, my invention results in an increase of almost 50% in the yield of recovered naphthalene. This advantage cannot be achieved in the absence of the separation of the expressed oil into two portions, as described above.

Since the economies of the pressing operation depend to a large extent on the recovered yield of naphthalene, it will be understood that my invention represents a considerable advance over the prior art.

It thus will be seen that the objects of this invention have been fully and effectively accomplished. It will be realized, however, that the foregoing specific embodiments have been shown and described only for the purpose of illustrating the principles of this invention and are subject to change without departure from such principles. Therefore, this invention includes all modifications encompassed within the spirit and scope of the following claims.

This applicaiton is a continuation-in-part of my copending application, Serial No. 441,151, filed July 2, 1954, now abandoned.

I claim:

1. In a continuous process for the production of crystalline naphthalene from naphthalene oil suitable for hot pressing material by passing said oil through a pressing zone to remove said oil and thereafter recovering said naphthalene, the steps comprising (1) cooling said naphthalene oil to a temperature less than 60 C. to form naphthalene crystals therein, (2) passing said cooled naphthalene oil and crystals through a pressing zone, (3) constantly applying pressure to said crystals in said pressing zone and extruding naphthalene crystals from the exit end of said zone, (4) removing from a first region of said zone an oil fraction low in naphthalene content and rich in thionapthene, (5) removing from a subsequent region of said zone an oil fraction rich in naphthalene and (6) thereafter admixing said fraction rich in naphthalene with untreated naphthalene oil and cycling the resulting mixture to said pressing zone, for treatment according to the aforementioned steps (1) through (6).

2. The process of claim 1 wherein said second portion rich in naphthalene is cooled before being admixed with untreated naphthalene oil.

3. In a continuous process for the production of a highly purified naphthalene from naphthalene oil, having a solidification point between 60 and C., wherein said oil, after cooling, is passed through a pressing zone to remove at least part of the oily portions therefrom, and solid pure naphthalene is recovered, the steps which consist essentially in (1) cooling said naphthalene oil to a temperature within the range of between about 25 C. and 60 C., (2) passing the solidified naphthalene oil through a pressing zone having foraminous walls, and applying pressure to the same by turning an axially mounted rotatable worm press therein, (3) expressing as a result of said applied pressure oil through the perforations of said foraminous walls along the entire length of said pressing zone, (4) collecting a first portion of said expressed oil from the first region of pressure application of said naphthalene oil, said first portion being low in naphthalene content and rich in thionaphthalene content, (5) removing a second portion of the said expressed oil from a subsequent region of said zone, said second portion being an oil fraction rich in naphthalene, (6) thereafter admixing said second portion, rich in naphthalene, with untreated feed naphthalene oil, and cooling the mixture, (7) thereafter recycling said cooled mixture to said pressing zone for further treatment by the aforesaid steps, whereby pure solid naphthalene is recovered at the end of said pressing zone with a solidification point of at least 79 C.

References Cited in the file of this patent UNITED STATES PATENTS 675,179 Wacker May 28, 1901 2,162,564 Poliner June 13, 1939 2,321,117 Wilcock June 8, 1943 2,331,883 Anderson Oct. 19, 1943 2,683,178 Findlay July 6, 1954 2,701,518 McDonald Feb. 8, 1955 2,747,001 Weedman May 22, 1956 2,780,663 Gunness Feb. 5, 1957 2,781,294 McKay Feb. 12, 1957 2,795,635 McBride June 11, 1957 FOREIGN PATENTS 493,992 Great Britain Oct. 18, 1938 

1. IN A CONTINUOUS PROCESS FOR THE PRODUCTION OF CRYSTALLINE NAPHTHALENE FROM NAPHTHALENE OL SUITABLE FOR HOT PRESSING MATERIAL BY PASSING SAID OIL THROUGH A PRESSING ZONE TO REMOVE SAID OIL AND THEREAFTER RECOVERING SAID NAPHTHALENE, THE STEPS COMPRISING (1) COOLING SAID NAPHTHALENE OIL TO A TEMPERATURE LESS THAN 60*C. TO FORM NAPHTHALENE CRYSTALS THEREIN, (2) PASSING SAID COOLED NAPHTHALENE OIL AND CRYSTALS THROUGH A PRESSING ZONE, (3) CONSTANTLY APPLYING PRESSURE TO SAID CRYSTALS IN SAID PRESSING ZONE AND EXTRUDING NAPHTHALENE CRYSTALS FROM THE EXIT 